use of aqp::rgb2munsell() in soilDB

[dylanbeaudette]

I'm about to push aqp 2.0.2 out which will start the transition from rgb2munsell() → col2Munsell(). I've made this change to all aqp functions and documentation. Prior to aqp 2.1 a message will be issued when rgb2munsell() is called, after that it will be deprecated. col2Munsell() is a more generalized version with better error trapping, and eventually, better documentation than rgb2munsell().

I've added some TODOs in soilDB as reminders to myself, once aqp 2.0.2 is on CRAN.

related issue in aqp

[brownag]

closed by #325